The invention is based on an apparatus for detecting the fuel quantity delivered to the combustion chambers of a Diesel engine. In the specification for prior art apparatus, it is stated that not only is the height of the pressure in a fuel line leading to the injection valves important for diagnostic purposes, but also the instant of appearance of pressure pulses which provide information as to the instant of fuel injection. The same is true for the duration of a pressure pulse, on the basis of which it is possible to ascertain the injection quantity per injection procedure if the injection pressure is known. Finally, the frequency of the pressure pulses repesents a standard for the rpm of the internal combustion engine.
With a view to the desired regulation of an injection nozzle's injection onset or of the supply onset of an injection pump, as well as of the injected fuel quantity, strenuous efforts must be made to detect these values as precisely as possible. In the known apparatus the individual pressure signals are evaluated in direct fashion for this purpose. However, it has been demonstrated that the known diagnostic apparatus is not always capable of producing satisfactory results for all operational states; for instance, resonance in the pressure lines causing sound and pressure line resonance signals and scattered interference cause measurement errors.